At idle, it’s the AMD’s Athlon X2 4850e and 740G that serve up the lowest power consumption numbers. Stepping up to a quad-core Phenom X4 at the same frequency costs an extra 30 W. Intel’s Core 2 Duo E7200 falls in between the two, using nine more watts than the ultra-efficient 4850e.
Pour on the load, however, and power consumption gets a bit more interesting. The Intel chip actually uses the least power at 115 W. The Athlon X2 4850e jumps up to 127 W. And the Phenom X4 eats up 230 W total (from the wall, of course).
So, not only are there important price and performance considerations to factor into your buying decision, but power puts an twist on things as well. Dual-core processors are naturally going to use less energy at comparable frequencies. The difference can actually get pretty significant, though, once you start cranking up the workload.